Question

I’m using the jackson library to map JSON into objects. I’ve simplified the problem a lot, this is what happens:

public class MyObject{

    public ForeignCollection<MySecondObject> getA(){
        return null;
    }

    public ForeignCollection<MyThirdObject> getB(){
        return null;
    }
}

I’m parsing the an empty JSON string:

ObjectMapper mapper = new ObjectMapper();
mapper.readValue("{}", MyObject.class);

On readValue, I get this Exception:

com.fasterxml.jackson.databind.JsonMappingException: Can not find a deserializer for non-concrete Collection type [collection type; class com.j256.ormlite.dao.ForeignCollection, contains [simple type, class com.test.MyThirdObject]]

This happens when I have two get methods in the MyObject class which return a ForeignCollection. Removing one of the get methods results in no exceptions.

I’m actually surprised by the fact that the mapper looks at the get methods, it should just set the fields I indicate.

What is happening here?

Answer 1

I’ve fixed this by converting the ForeignCollection to a List:

private ForeignCollection<MyObject> myObjects;

public List<MyObject> getMyObjects(){
    return new ArrayList<MyObject>(myObjects);
}